Combination weighing systems of the type having a plurality of circularly arranged weigh hoppers are well known. For example, the Henry et al. Patent No. 4,418,771 discloses a system wherein a predetermined weight of product is made up of individual articles of varying weights. In the Henry method and apparatus, the predetermined weight is reached by selecting the product stored in a combination of a predetermined number of storage cups. Quantities of the product having targeted weights are distributed to a plurality of scale-controlled hoppers for accurate weighing. The weighted product is fed from each of the scale-controlled hoppers to a plurality of storage cups associated with each of the hoppers, and the product weight associated with each storage cup is registered. Specific combinations of storage cups are tested to determine whether the combined product weights therein add up to make the desired weight, within acceptable limits. The first combination found to make the weight is used, and the appropriate storage cups are emptied to a container for receiving the product. The appropriate storage cups are refilled from the scale, and the process repeats. When none of the combinations of the preselected number of storage cups include a total product weight within the acceptable limits, the limits are broadened and the cycle repeats. The weighing system includes a programmed microprocessor for controlling operation thereof, for providing the combination to be tested, for calculating the combined weights, and for determining whether the combined weight falls within the acceptable limits. A distributor for the product includes a reversing rotating portion for preventing clogging of the product at openings provided for chutes connecting the distributor to the scale-controlled hoppers.
A more recent approach to an improved combination weigher is disclosed in the U.S. Pat. No. 5,211,253 of Thornton Davis which is assigned to the same assignee as the present application and which is incorporated herein in its entirety by reference. As disclosed by Davis, the apparatus comprises means including a plurality of balances each of which is adapted to receive and weigh a fraction of the collection and unload product therefrom to contribute to a delivery. The apparatus also includes means for recording a predetermined target weight and control means for determining which of the balances are in a ready or stable state. Means are also provided for generating the values of combinations of weights on the balances which are in the ready state and for comparing the values with the predetermined target weight and for selecting a combination of balances to be unloaded to deliver a collection of articles having a combined weight which most nearly approximates the target weight. In practice, it may be desirable to select those scales having a combined weight which is at least equal to the predetermined weight to avoid any underweight packages. The apparatus also includes package positioning and signal generating means such as a packaging machine for positioning a package to receive a collection of articles from the selected balances and for generating a signal to indicate that a package is positioned to receive the articles from the balances. Means for unloading the balances of the selected combination for delivery of the product contained therein to a properly positioned package are also provided. Means for generating the values of combinations of weights on the balances which are in the ready state including the originally selected balances and any balances which have reached a ready state subsequent to a first comparison are actuated for comparing the values with the predetermined target weight. In this manner, all of the ready balances are included in the comparison and a second selection having a weight which most nearly approximates the target weight is delivered to a package. Means are also provided for refilling those balances which have been unloaded.
The aforementioned combination weighers normally incorporate a distribution system for delivering solid flowable product to the plurality of scales. In such systems, a cone shaped member is located directly above the infeeds for a plurality of conveyors which direct the product to the various scales. In such devices, a relatively deep pile of product may form on the cone shaped member and cause non-uniform feeding. One approach to overcome this problem is disclosed in a co-pending U.S. patent application entitled, A Distribution System for a Combination Weigher or the Like, Ser. No. 08/178,852 in the name of Richard Stapp and Glen Hayes. That application is assigned to the same assignee as the present invention and is incorporated herein in its entirety by reference.
The aforementioned application overcomes to a large degree the problems associated with prior art distributors, but does not address a particular problem associated with combination weighers wherein the portions being weighed have a relatively low piece count. Low piece counts refer to those portions which are made up of less than about 20 pieces. The problem associated with such counts is to control the product feed so that only 3 or 4 pieces of product are deposited in a weigh bucket for each cycle. One approach to solving this problem includes shaping the vibratory conveyor to provide a thin narrow stream of product to provide a consistent result. However, the effectiveness of the shaped conveyors varies depending on the shape of the product. For example, when the product has edges that tend to bridge, narrow feeders are unsatisfactory.
It is now believed that there is a significant demand for an improved conveyor for a combination weigher or the like. The demand is for a conveyor which will consistently deliver low piece counts to each of a series of scales. The conveyor should also remain consistent for different types and sizes of products, minimize down time for change over to a different product, be relatively simple in design and relatively inexpensive to manufacture. It is also presently believed that an improved conveyor in accordance with the present invention has all of the aforementioned characteristics.